This application is related to and claims priority from Japanese Patent Application No. 2002-257878 filed on Sep. 3, 2002, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an air passage switching device for switching and controlling a communication state of an air passage by moving a film member in the air passage. The air passage switching device is suitably used for a vehicle air conditioner.
2. Description of Related Art
An air passage switching device for switching an air passage by moving a film member is disclosed in JP-A-8-2238. In this air passage switching device, both ends of the film member are connected to a driving shaft and a driven shaft, respectively. In this way, the film member is wound around one of both shafts and is wound off from the other thereof. Thus, the driving and driven shafts are required to be rotated while being operatively linked to each other, and a link mechanism such as a pulley and a wire is required. As a result, the number of components of the air passage switching device is increased, and assembling operation is complicated, thereby increasing production cost of the device.
In view of the above problem, U.S. Pat. No. 6,508,703 (corresponding to JP-A-2002-79819) proposes a simple air-passage switching device without using a link mechanism. In this air passage switching device, the film member is moved so as to be extruded. However, the film member may be buckling-deformed and damaged when being extruded. Further, the film member may be permanently deformed when being left in the buckling-deformed state for a long time. In this case, a clearance is caused between the film member and an outer peripheral portion of an opening that is opened and closed by the film member. Therefore, air leaks from the clearance, sealing performance of the film member is reduced, and the air passage cannot be closed by the film member.
In view of the above-described problems, it is an object of the present invention to provide an air passage switching device capable of restricting its film member from being damaged.
It is another object of the present invention to effectively reduce an air leakage amount in the air passage switching device.
According to the present invention, an air passage switching device includes an air duct for defining an air passage through which air flows, a flexible film member being movable to traverse the air passage for switching and controlling a communication state of the air passage, and a driving unit that extrudes the film member so as to move the film member. In the air passage switching device, the film member has a bending stiffness equal to or larger than 1 xcexcNxc2x7m2. When the film member has the bending stiffness equal to or larger than 1 xcexcNxc2x7m2, a bucking-generation operation force for causing a buckling-deformation of the film member is larger than a general operation force for moving the film member. Accordingly, it can restrict the film member from being buckling-deformed, and from being damaged. Generally, the film member is made of resin.
Alternatively, in the air passage switching device of the present invention, the film member has a thickness t (mm), a glass transition temperature Tg (xc2x0 K) and a radius of curvature r (mm) so that a relationship expressed by a formula of txe2x89xa6(0.00578xc3x97Tg0.448xc3x97r0.333) is satisfied. In this case, it can effectively restrict a deformation of the film member, thereby effectively reducing an air leakage due to the deformation in the air passage switching device.
Preferably, the air duct has a guide member for guiding a movement of the film member, and the driving unit includes a frame member provided in the air duct, a gear member provided in the frame member, and a driving member engaged with the gear member to move the frame member in a moving direction. Further, one end of the film member is connected to the frame member and the other end of the film member is a free end in the moving direction so that the film member is movable along the guide member in accordance with the movement of the frame member. Even this case, the air passage switching device effectively restricts buckling-deformation of the film member, and an air leakage due to the buckling deformation.